Anchoring cathode



May 16, 1950 J. KELAR 2,507,979

ANCHORING CATHODE Filed March 15, 1948 Inventor 4 49 4 J1: SEPI-I KELARPatented May 16, 1 950 ANCHORING CATHODE Joseph Kelar, Lancaster, Pa.,assignor to Radio Corporation of America, a corporation of Dela.-

ware

Application March 13, 1948, Serial-N0. 14,745

2 Claims.

My invention relates to electron discharge devices and in particular toan electron gun structure comprising an improved cathode for use in acathode ray tube or the like, and is a continuation-in-part of mycopending application Serial Number 757,633, filed June 27, 1947, nowPatent Number 2,443,916.

A conventional type of cathode ray tube has an electron gun structurecomprising in part a tubular cathode enclosing a heater filament andspaced critically from a control grid. Axially spaced along the gun fromthe control grid is a focusing grid plate, a first anode cylinder and asecond anode cylinder. These structures when maintained at appropriateelectrostatic potentials form a series of bipotential electron lenseswhich tend to form the electron emission from the cathode into a beamand accelerate and focus the beam on a fluorescent screen or at the endof the tube.

The construction of the cathode-grid structure of a conventional type ofelectron gun has previously involved the difiicult process ofassembling, by hand operation, many small parts in the properrelationships. The process also involves the fiXing of severalsub-assemblies in a predetermined spaced relationship involving criticaldistances conforming to small tolerances.

In practice, the cathode structure for a cathode ray tube or for sometypes of high frequency tubes having an indirectly heated cathode,comprises a cylindrical cathode tube mounted through an annular ceramicdisc. The cathode tube is fixed to the ceramic by flanged rings slippedover each end of the cathode and welded to the cathode sleeve inabutment to the ceramic. Ordinarily, the emitting surface of the cathodeis axially spaced from the control grid by a predetermined criticaldistance within very close tolerances. This cathode-to-control gridspacing is determined by the axial dimension of a spacer elementpositioned between the top surface of the cathode support ceramic andthe control grid plate, as well as, the axial distance between theemitting surface of the cathode and the top surface of the cathodesupport ceramic. It has been diflicult in the past to fix the cathodetube to its supporting ceramic with the required distance between theemitting surface of the cathode and the upper surface of the ceramicsupport.

It is therefor anobject of my invention to provide an electron gunstructure of improved design.

It is also an object of my invention to provide an electron gunstructure comprising a cathode assembly having few parts.

It is a further object of my invention to provide an electron gunstructure having a cathode assembly designed for rapid and accurateconstruction.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims, but theinvention itself will best be understood by reference to the followingdescription taken in connection with the accompanying drawing, in which:

Figure 1 is an elevational view partially in section of a portion of anelectron gun structure incorporating the cathode assembly according tomy invention;

Figure 2 is a sectional view of a cathode assembly according to myinvention;

Figure 3 is a sectional view in elevation of an apparatus for theassembling of the cathode structure according to my invention;

Figure 4 is a sectional view in elevation oi a modification of a cathodeassembly and a device used in its construction according to myinvention; and

Figure 5 is a sectional view in elevation of modification of a cathodeassembly.

Referring to Figure 1 there is shown an electron discharge device havinga glass envelope l0 closed at one end by a glass stem l2. This end ofthe discharge tube It! is enclosed by a conventional base structure I lhaving base pins l6 fixed thereto. Through the glass stem 12 of the tubeare sealed lead pins l5 to support the electrode structure within thetube and for forming conductive paths thereto. Fixed to two of the stemleads I 5 are two ceramic support side rods l8. Mounted on the side rodsI 8 immediately above the stem portion [2 is a control grid cylinder 20coaxial with the tubular envelope 10 of the discharge device. The upperend of cylinder 20 is closed by a grid plate 22 having at its center anaperture 24. Also, mounted on the support ceramic side rods 18 andaxially spaced along the tubular envelope 10 from the cylinder 20 is atubular first anode electrode 26 partially shown in Figure l. v

Mounted within the control grid cylinder 20 is a cathode tube 28 toprovide a source of electrons within the tube. The tubular cathodeelectrode 28 is closed at its top by a cap 29 closelyspaced from thegrid aperture 24 and coaxial therewith. Upon the top of cathode cap 29is deposited preferably a mixture of alkaline earth metal oxides toprovide a source of electrons when heated to an appropriate temperature.

For maintaining the electron emitting surface of the cathode cap 29 atthe desired temperature, a heater filament 25 is enclosed within thecathode tube 28. Passage of current through the filament 25 maintainsthe emitting surface of cathode cap 29 at a temperature sufficient toprovide an emission of electrons for tube operation. With properpotentials applied to electrodes 22 and 26 an electrostatic field isestablished which will form an electron beam. The electron beam may befurther focused and accelerated by other electrodes, not shown, toperform any desired function. Such an electrode assembly structure asshown in Figure 1 may be utilized in a cathode ray tube or in any othertype of electron beam tube. Furthermore, the type of cathode structureto be described below may be used in other types of discharge devicesand should not be considered as confined, by its operation and design,to a tube having a structure similar to that of Figure 1.

Figure 2 shows a preferred form of a cathode assembly similar to thatdescribed in Figure l. The cathode assembly of Figure 2 comprises atubular cathode sleeve 28 having one end closed by cap 29 fixed thereto.The tubular cathode is supported by an annular insulating ceramic disc36, having an opening or aperture 3! at its center. The tubular cathodesleeve 28 is mounted within the apertured portion 3|, so that theinsulating support member 38 fits the tubular walls of the cathode 28 ata portion between the ends of the cathode tube. Cathode tube 28 is alsopreferably mounted coaxial to the ceramic disc 30. Means are providedfor locking tubular cathode 28 to the insulating support 38 in order toprevent any relative movement axially between tube 28 and disc 38. Theselocking means preferably comprise peripheral ribs or embossments 38 and40 which are pressed outwardly from the sur- 1 ace of the tube 28,respectively below and above the ceramic support 38. The ribs orembossments 38 and 48 are forced outwardly until they abut against theceramic 88 to tightly loci: cathode tube 28 within the aperture 3|.

The outwardly projecting ribs 38 and 48 on the cathode sleeve 28 may beformed in various ways. Also, it is not felt that the structure ofFigure 2 need necessarily be limited to the particular type ofembossment or ribs shown. It is conceivable that any type of projectionfrom the surface of the cathode tube 28 may be substituted for the ribs38 and 40. For example, the outwardly extending projections 38 and 48may take the form of flaps cut in the wall of the cathode 28 and bentsharply outward both above and below the ceramic 30 to tightly hold theceramic to the cathode tube 28.

In Figure 3 there is disclosed a device and method for expanding thewalls of the tubular cathode to form the projecting ribs 38 and 40. InFigure 3, is a cathode sleeve 42 similar to cathode 28, of Figures 1 and2. Sleeve 42 may be formed by using a single piece of metal and with theproper handling the metal may be drawn into a one piece cup having anenclosed end 49. The cup is threaded through the apertured center of theceramic support disc 38. A spacer block 48 is used having apertures 45and 41 therethrough. The opening 47 in the upper side of the spacerblock 46 is shown in Figure 3 to be circular and of a size that theceramic disc 38 may be fitted coaxially therein. The opening 45 is alsoa circular opening coaxial with aperture 41, and is of a size to freelyreceive the closed end of the cathode tube 42. Since the two openings 45and 4! are of different radii, a shoulder is formed therebetween. Thecathode sleeve 42 and ceramic support 30 fitted thereto are placedwithin the apertured portion of block 46 with the closed end 49 ofcathode sleeve 42 enclosed within the apertured space 45 and the ceramicspacer 30 upon the shoulder portion 5|. A tool used for forming the ribs4| and 43 comprises a sleeve 48 fastened in the ram of an arbor press ora drill press 62.

Floatingly mounted within sleeve 48 is a pin 50 having at its lower enda nailhead shaped part 54-. A washer 52 fixed to the upper end of pin 50prevents the pin from escaping through the sleeve 48. Mounted around thepin 58 and below the nailhead 54 and sleeve 48 are three washers orrings 58, 58 and 80. Washers 56 and 58 are of gum, rubber, andappropriate plastic or of any material having sufficient resiliency thatthe washers may be deformed by the application of pressure betweensleeve 48 and the nailhead 54. Washer 65 may be of a material havingrelatively no resiliency such as steel but preferably is formed of ahard material having some slight resiliency or give.

The spacer block 45 together with the cathode assembly 8842 fittedtherein is placed upon a smooth metal base plate 44 directly under thearbor press Sleeve 43' is then inserted into the tubular cathode 42 bythe downward motion of the arbor press 52. Pin 58 and the washers 58 and558 ride downwardly within the sleeve until the nailhead contacts theinner surface of the closed end 48 of the cathode tube. With the ceramicspacer 38 resting upon the shoulder portion 5! of the spacer 45, furthermovement of the sleeve 48 forces the cathode cup tightly against thesmooth surface 44. When the downward motion of nailheaded pin 58 isstopped, further downward movement of sleeve 48 compresses the washers58 and 58 and forces washers 5'5 and 58 out at the sides against thewall of the cathode tube 42. Tubular cathode 42 is sufficiently thin tobe deformed by the pressure of the washers and 58, when they arecompressed between the sleeve 48 and the nailhead 54. The wall of thetubular cathode 42 is pressed outwardly by this action into abutmentwith the edges of the aperture 3| of the ceramic 3D and is formed intothe two peripheral locking rib portions GI and 43. Thus, the ceramic 38is firmly gripped and tightly held between the expanded portions ll and43 of the cathode sleeve.

The axial dimension of nailhead 54, as well as,

; that of the hard washer 88 is so chosen that ribs 4! and 43 arepressed outwardly at the proper points to firmly grip the ceramic 38therebetween. Washer may be made of steel but I have found that improvedresults are obtained when a hard rubber washer is substituted. The hardrubber washer 58 is slightly compressed, when pressure is applied to thewashers 56 and 58, to cause a radial expansion thereof. This slightexpansion of the hard washer 50 causes it to fit tightly within thetubular cathode 42, while the rib portions 4| and 43 are being formed.This has an advantage, in that, during rib forming operation, there isno free space existing between the washer 68 and the inside of thecathode tube 42. This prevents the softer rubber of washers 58 and 58from being forced between washer G0 and the tube wall, and thus reducesexcessive wear on washers 5B and 58.

In Figure 1, it is seen that the cathode cap 29 is spaced from the gridplate '22. This cathodeto-grid spacing is rather critical and shouldvery closely conform to a predetermined distance. Cathode 28 is spacedfrom the grid plate 22 by a spacer ring or eyelet 32. Thecathode-to-grid spacing is determined by the axial dimension of theannular spacer ring 32 as well as the distance between the upper surfaceof the support ceramic 38 and the electron emissive surface 29. It canbe seen from Figure 1 that the critical cathodeto-grid spacing dependsupon the accuracy with which the annular spacer 32 is made, as well as,the accuracy with which the cathode tube 28 is positioned relative tothe ceramic disc 32.

In Figure 3, the spacer block 46 is chosen with an axial depth ofaperture 115 which will provide the required distance that the end 49 ofthe cathode is to be positioned from the surface of the support ceramic3c. The use of the arbor press 92 forces the cathode sleeve 42 tightlyagainst the smooth surface 44 and when the ceramic disc 39 is suportedby the shoulder portion 5|, the proper distance between the closed end49 and the ceramic 30 is maintained while locking ribs 4| and d3 areformed.

Figure 3 thus discloses a method as well as a means for accuratelypositioning the cathode tube 42 relative to its supporting ceramic 30and for locking the cathode assembly together. This method of assemblingthe cathode sleeve 42 and its ceramic support 39 eliminates the use ofother elements and parts, similar to the flange ring 58 of Figure 4, forexample, which have been used in the past to lock the supporting ceramicto a cathode sleeve. Furthermore, the positioning of cathode G2 at thepredetermined relationship to its supporting ceramic 30 and the lockingof cathode 415;. to its supporting ceramic 30 may be accurately andsimply accomplished by one operation.

The design of the cathode disclosed in Figures 1, 2 and 3 should notnecessarily be limiting, as it is possible to use this method of lockinga cathode sleeve to a ceramic, with cathode structures of differentdesign. For example, in Figure 4 there is disclosed a cathode sleeve 64closed at one end by a cap 55. A flanged washer 68 is slipped over theopen end of the cathode and welded at a predetermined position to theouter surface of the tubular cathode 54. The position at which theflanged ring 98 is fixed to the cathode sleeve determines the spacingbetween the ceramic 39 and the activated surface on top of the cathodecap 56. The ceramic disc support member 30 is slipped over the open endof the cathode sleeve E i until it abuts against the flanged ring 38 andis locked, in this position, by forming a rib or embossed portion orportions 10, projecting outwardly to firmly press ceramic disc 30tightly against the flanged ring 88 and also prevent any axial movementbetween the ceramic 30 and the cathode sleeve 65. The embossment l9placed in the cathode wall may be formed by a tool similar to that shownin Figure 3. For example, the tool may comprise of a stationary sleeve12 surrounding a pin 74 having a nailhead 76 at one end. Between thenailhead l6 and the adjacent end of sleeve 12 is positioned a resilientwasher 18, preferably of deformable rubber. The sleeve 12 together withthe pin 14 and the washer I8 therebetween is inserted into the open endof cathode sleeve 64 at an appropriate distance. The inner pin is thenforced downwardly while the sleeve 12 is held stationary. The downwardmotion of the nailhead 16 tends to compress the resilient washer 18between it and sleeve 12. The thin wall of the cathode sleeve 64 willbulge outwardly and form the ribbed or embossed portion 10.

Figure 5 shows a modification of the cathode assembly shown in Figures1-4. This cathode sleeve 80 may consist of a metal tube open at bothends, one end of which is closed by a cap 82. However, as shown inFigure 3 the cathode tube of Figure 5 may also be drawn from a singlemetal piece, so that a cathode cup is formed closed at one end. Such adrawing operation would eliminate additional structure, such as cap 82and assembly operations to fasten it to the cathode tube. The drawingmay be done with proper handling in a single operation. A ceramicsupport disc 54 is used in the modification of Figure 5. The support 34has an open center and is coaxially mounted on the tube 89 by slippingthe ceramic over the open end of the cathode tube.

A groove 85 is channeled in the surface of the central aperture of theceramic support 86. When the ceramic o l is properly positioned on thecathode sleeve 80 an embossment or rib 88 is formed in the tubularcathode wall in a manner that the rib 38' will bulge outwardly andproject into the channeled groove 86. Rib 38 may be formed in anydesired manner such as that suggested in the method disclosed relativeto Figure 4. However, the wall of the metal is bulged outwardly to suchan extent that the metal of the wall is made to tightly fit into thechanneled groove 86. If desired, rib portions may be formed above andbelow the ceramic disc 84 similar to embossments 33 and iii of Figure 2.However, the rib 85, if properly formed, is sufiicient to firmly lockthe ceramic 8A to the cathode tube 80.

While certain specific embodiments have been illustrated and described,it will be understood that various changes and modifications may be madetherein without departing from the spirit and scope of the invention.

What I claim as new is:

l. A cathode electrode assembly for an electron discharge device, saidcathode assembly comprising a cathode tube, an insulating support havingan aperture, said aperture having a channel formed in the inner surfacethereof, said cathode tube coaxially mounted within said aperture, andmeans locking said cathode tube to said insulating support, said lockingmeans including a portion of the wall of said cathode tube pressedoutwardly into engagement with said channel.

2. A cathode electrode assembly for an electron discharge device, saidcathode assembly comprising a cathode tube, an annular insulatingsupport disc coaxially mounted between the ends of said cathode tube,said annular disc having an aperture therethrough and a peripheralgroove in the surface of said aperture, and means locking said supportdisc to said cathode tube, said locking means including a portion of thewall of said cathode tube pressed outwardly as a rib into engagementwith said peripheral groove.

JOSEPH KELAR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS- Number Name Date 2,067,967 Kniepen Jan. 19, 19372,244,358 Ewald June 3, 1941 2,306,018 Fentress Dec. 22, 1942 2,393,057OLarte et al Jan. 15, 1946 2,405,399 Bugg et al Aug. 6, 1946 2,417,202Hull et al Mar. 11, 1947 2,460,580 Huber Feb. 1, 1949

